Hydrocarbon-based fuels are available from a variety of sources including biogas from landfills, wastewater treatment plants, agricultural and other digesters, light hydrocarbon gases from oil and gas wells, and various heavier hydrocarbon gases from processes such as refinery processing. These fuels can be used in an engine to generate electricity and heat. These fuels can be combusted either in a gas turbine engine (Brayton cycle), an internal combustion engine (Otto cycle), or other prime-mover engines (e.g., Sterling engines). Any of these engines can be connected to an electric generator to generate electricity or a shaft to provide shaft power for a variety of applications. The electric generator would produce electricity, which could either be exported to the electric utility grid (grid-parallel) or used locally to power various on-site electric loads (grid independent). Waste heat from the combustion process can also be used to heat water or other fluids.
The fuels from the above-mentioned sources contain constituents and contaminants that can cause problems in the fuel system, and/or the engine. In addition, most engine combustion systems react fuel and air at elevated pressures. Thus, the fuel gas must be compressed to a higher pressure to be admitted into the engine for combustion.